voltage sensing relay?

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=31248
Printed Date: May 10, 2025 at 12:02 AM

Topic: voltage sensing relay?

Posted By: sitinduk
Subject: voltage sensing relay?
Date Posted: April 28, 2004 at 11:45 PM

Hi, is it possible to set up a relay that will activate only at a certain voltage? For instance, say terminal 86 is connected to ground, and 85 is connected to a wire that varies from 0.5V to 4.8V. I only want the relay to activate its circuit when 85 sees 4.8V.

Replies:

Posted By: xetmes
Date Posted: April 29, 2004 at 5:47 AM

You could use electronics to scale the voltage, or use an analog to digital conversion, but with just a relay it may be tricky or unreliable.Can I ask what the purpose is?

Posted By: sitinduk
Date Posted: April 29, 2004 at 8:37 AM

I was going to make a switch for a custom nitrous oxide setup. I wanted the nitrous and fuel solenoids to open only at wide open throttle. The throttle position sensor varies its voltage from 0.5V at closed throttle to 4.8V at WOT. They make mechanical switches for this purpose, but I wanted to go with something electric.

Posted By: xetmes
Date Posted: April 29, 2004 at 6:25 PM

hmm is this just a DC voltage? I dont know enough about the TPS...

If it is just DC:

You could use a differential type amplifier like an opamp and compare the value to a reference voltage and detect when the difference is 0V.

Or you could use a programmable controller and use analog to digital conversion and compare it in the digital world, that would be my preferred choice.

Posted By: sitinduk
Date Posted: April 29, 2004 at 9:42 PM

The TPS is just DC. I'll have to look into a programmable controller.

Thanks for your help.

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